Fuelling problems

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Fuelling problems

Post by ianm » Thu Jul 11, 2019 1:10 pm

Some of you may be aware that I have had occasional fuelling problems on my 289 especially at Le Mans Classic last year when it was very hot. Although the pump could be heard running it turns out that there was very little flow even before the filter king. There was also 12 volts at the pump so there was a tendency to blame the pump. Substitution of the pump had no effect. All lines were clear and gravity showed plenty of flow from the tank. The only other variable was the electrics which I pursued back through the rear loom connector behind the dashboard and then on to the immobiliser where I had the fuel pump circuit connected. Bridging the connector has solved my nagging problem at last and the fuel pump sounds more akin to a pump again while delivering plenty of pressure.
I dont know why the immobiliser did not allow sufficient current on that circuit but hope my result is of interest and worth bearing in mind if you have problems with circuits that you have connected to your immobiliser. It is easy to 'forget' that it is in some circuits.

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Re: Fuelling problems

Post by KevinW » Thu Jul 11, 2019 6:26 pm

If your immobiliser is the standard Toad /Stirling unit that many people use, the answer is the wiring. Mine came with a long run of fairly thin black wire. I immediately cut this off and replaced, via a multi-way connector, with decent gauge wiring runs for the circuit I wanted to interrupt. Some of the runs can be several meters long, and I am aware of others who have had problems with immobilisers that simply failed to work....nothing wrong with the unit: length of thin black wire was too long for the required current. This can be resolved with heavier gauge wire.

In fact long runs with thin wire carying too large a current load can be a fire hazard on a grp car: when there is significant voltage drop along the length of the wire for long periods, then the wire simply acts like a heater, or worse, when overloaded.

For more information on this, and an on-line calculator see;
https://www.12voltplanet.co.uk/cable-si ... ction.html

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Re: Fuelling problems

Post by amulheirn » Fri Jul 12, 2019 5:16 pm

Thanks for this info Ian and Kevin.

I have the Stirling one, and was surprised at the thinness of the wires. I didn't cut them down at all, but am thinking I might do now!


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John H
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Re: Fuelling problems

Post by John H » Sat Aug 03, 2019 6:10 pm

Thanks Ian for the info. On the way to Silverstone classic this year and after a long time in traffic on a hot day my car just stopped. It sounded like fuel starvation or evaporation. I pulled over and lifted the bonnet to cool a while. After 20 mins she started and I rejoined the traffic! I only went around 300 meters to join the A34 before she cut out again on the slip road. This time she would not restart or even turn over the starter motor. I noticed the immobiliser light just dimly flicker when she cut out. So I was stranded on the slip road with very heavy traffic on the A34 on a busy Friday afternoon. I lifted the bonnet and waited for her to cool. Fortunately I still had my emergency triangle from my trip to France last year and used it to protect the car from folk joining the road and looking at the on coming traffic rather than the cobra stranded right in front of them, I had a couple of near misses!

After about 40 mins she still had no pump or started motor on the key turn. I felt the bulkhead where I have the immobiliser fitted. It was still very warm I would estimate at 40 or 50 deg C! I speculated the bolts were transmitting the heat directly to the metal immobiliser case inside the car. I poured some water over the bulkhead and waited another 20 mins.
I was toying with the idea of calling Greenflag but thought I would try once more. She fired up immediately! The traffic was still stop start and it was still very warm so I waited until it was moving well before joining. I was lucky to get into another lay-by as the traffic came to a halt again before rejoining and getting off the road. She was fine all weekend after that. She did the same thing when I stopped at Newcastle on the way home but water again did the trick! So I am not sure if its just heat that is causing the problem. I had no problem in France last year as Ian did but I don't think I was in anywhere near as much slow moving traffic.
So I intend to find a way of insulating the immobiliser in its current location or moving it away from the bulkhead. I may wait until the winter though as I suspect I won't have the problem here in Scotland now!
I too have not modified the Sterling wires, they are very thin. Maybe something I will consider in the future.
Built St Piran Hawk289FIA in Scotland!

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Re: Fuelling problems

Post by Jerryedmans » Mon Aug 05, 2019 12:12 pm

Interesting. I have a Sterling Toad immobiliser and agree wires look very thin especially for fuel pump, but so far has been ok. Occasionally it takes a couple of attempts for it to recognise the immobiliser tag when starting but otherwise working. A fuel pressure gauge would presumably help to see if pump delivering pressure.

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